There is increasing use of apparatus of a type in which a switched telephone network (hereinafter "STN") is connected in parallel with a conventional telephone instrument. Such items of apparatus commonly employ a modem connected to the STN line to modulate or demodulate the data to be sent or to be received. However, apparatus now exists, such as certain digital television decoders, which uses a modem to establish a connection back to the program provider. In such digital television decoders, it is common practice to establish the connection back to the service provider at night time so as to avoid any inconvenience to the user.
The viewer therefore risks finding the telephone line busy when he picks up the handset. This can be inconvenient and even dangerous when an urgent call has to be made.